Hi, Thank you for the soft it's very nice!
So I suggest:
1- an enharmonic button. For example if i'm in key of C major i can't write a Bb (only a a#).
2- If it's possible, importing lilypond file. For example if i export a project in lilypond and i correct some things i can't import this in TuxGuitar.
3- For the moment i don't find how to write two voice in a same staff. For example two quarter notes on a half note.
Thank you again.